A display device for a vehicle called a head up display projects display light representing a display image emitted from a display onto a front glass or a dedicated combiner, and enables an observer (mainly, a driver) to recognize a virtual image of the display image superimposed on a scene viewed through a front glass or the like. On the other hand, a height of observer's viewpoint is not constant due to differences in physique and driving posture. Thus, it is necessary to adjust a projection point of display light in a vertical direction depending on the height of observer's viewpoint to enable the observer to recognize a virtual image even when the height of observer's viewpoint changes. As a conventional method of compensating for differences in the height of observer's viewpoint, a head up display disclosed in Patent Literatures 1 to 3 is known.